Absolute encoders are known for providing an output indication of the position of a sensing head relative to a measuring scale. For sensing rotary displacement, the scale is in the form of a disc with one or more tracks with one or more sensors per track. For sensing linear displacement, the scale is an elongated member containing one or more linearly arranged parallel tracks with one or more sensors per track. The tracks are often formed of optically responsive segments, which segments are light transmissive or light reflective, but the tracks can alternatively be of other forms such as magnetic, capacitive or inductive. Higher resolution is achieved by increasing the number of tracks.